1. Field of the Invention
The present invention relates to an apparatus and method for correcting a color error, and more particularly, to an apparatus and method for correcting a color error in a DLP system, which is capable of correcting the color error caused by temperature change.
2. Description of the Related Art
Recently, an image display device has been lightweight, slim and large-sized. Also, as a projection TV having a large-sized screen is manufactured at a low cost, its demand is increasing.
The projection TV projects an enlarged image on a screen, allowing a user to view a large-sized image.
Such a projection TV includes a cathode ray tube (CRT) projection TV, a liquid crystal display (LCD) projection TV, a digital light processing (DLP) TV, and so on.
Among them, a digital micromirror display (DMD) developed by Texas Instruments Incorporated is mounted on the DLP projection TV. Thus, the DLP projection TV can solve the disadvantages of the LCD projection TV that employs a thin film transistor (TFT) LCD. That is, the DLP projection TV can remove mosaic occurring in pixels and improve a reproducibility of an original color. Also, the DLP projection TV has a wide viewing angle and a high contrast ratio and can obtain a large-sized image having high-brightness and high-definition. For these reasons, the DLP projection TV is spotlight.
The DMD used in the DLP projection TV includes about nine hundred thousand micromirrors or more, which can be individually controlled.
A white light emitted from a lamp is converted into RGB primary colors through a color wheel coated with RGB color filters. The RGB primary colors are reflected according to motions (±15°) of the respective pixels contained in the DMD, thereby displaying an image on a screen.
A structure and an operation principle of the color wheel used in the DLP system will be described below with reference to FIG. 1.
Referring to FIG. 1, the color wheel 120 used in the DLP system includes a total of six segments, two segments each for R, G and B.
A motor 122 rotates the color wheel 120 according to a synchronization signal of an image signal, such that the white light emitted from the lamp is converted into R, G and B lights.
In order to accurately control the driving state of the color wheel 120, a color wheel index mark (CWIM) is marked on the color wheel 120. Also, a sensor 124 for sensing the CWIM is installed in the motor 122.
Since the CWIM sensing signal sensed by the sensor 124 represents a rotating speed and a rotating state of the color wheel 120, the color wheel 120 can outputs R, G and B lights matched with the synchronization signal of the image signal by detecting a phase difference between the CWIM sensing signal and the synchronization signal and controlling the driving state of the motor 122 according to the detected phase difference.
A method for controlling the color wheel 120 will be described below with reference to FIG. 2.
For the sake of convenience, the DLP system can be divided into an optical engine part and a data processing part.
The data processing part 100 includes a microprocessor 102, a memory 104, a data formatter 106, a phase difference detector 108, an index delay setup unit 110, and a pulse width modulation (PWM) control signal generator 112.
The optical engine part includes a DMD 114, a prism 116, a lamp 118, a color wheel 120, a motor 122, a sensor 124, a motor driver 126, a projection lens 128, a screen 130, and a ballast controller 132.
The microprocessor 102 controls an overall operation of the optical engine part and the data processing part 100 in the DLP system, and the memory stores a processing program of the microprocessor 102 and a variety of information.
The data formatter 106 encodes an image data and a synchronization signal into PWM bit sequence signals, which allows the DMD 114 to be driven. The data formatter 106 transmits the PWM bit sequence signal to the DMD 114.
The micromirror of the DMD 114 is turned on/off in response to the PWM bit sequence signal. An angle of the micromirror is shifted by ±15°, depending on the on/off states.
The color wheel 120 converts the light emitted from the lamp into R, G and B lights and provides the R, G and B lights to the DMD 114.
The prism 116 provides the lights passing through the color wheel 120 to the DMD 114. The micromirrors of the DMD 114 reflect the lights passing through the prism 116 to the projection lens 128, depending on the on/off states.
The projection lens 128 enlarges the lights provided from the DMD 114 and displays them to the screen 130. In this manner, the image is displayed on the screen 130.
Here, when the micromirrors are in the on-state, the light incident from the prism 116 is reflected within an effective screen. Meanwhile, when the micromirrors are in the off-state, the light incident from the prism 116 is reflected out of the effective screen.
The ballast controller 132 supplies a driving power to the lamp 118 under the control of the microprocessor 102.
The sensor 124 includes a photo sensor and a signal converter. The photo sensor senses the CWIM marked on the color wheel 120 so as to sense the driving state of the color wheel 120. Then, the signal converter converts the CWIM sensing signal into a digital signal and provides it to the index delay setup unit 110 and the microprocessor 102.
The index delay setup unit 110 delays the CWIM sensing signal under the control of the microprocessor 102 and provides the delayed signal to the phase difference detector 108.
The phase difference detector 108 detects the phase difference between the synchronization signal and the CWIM signal by comparing them, and provides the detected phase difference to the PWM control signal generator 112.
The PWM control signal generator 112 receives the phase difference information and generates a PWM control signal for correcting the phase difference to the motor driver 126.
The motor driver 126 drives the motor 122 to rotate the color wheel 120.
Like this, the related art DLP system can correctly reproduce the colors of the image signal by adjusting the phase difference between the synchronization signal and the CWIM sensing signal.
However, in the process of sensing the CWIM marked on the color wheel 120 and converting the CWIM sensing signal into the digital signal, the CWIM sensing signal is influenced by the temperature change.
That is, since the CWIM sensing signal is influenced by the temperature change, an error occurs in the rotating speed and the phase of the color wheel when the internal temperature changes, resulting in a color error.